CH. IX] OBJECTIONS TO THE HYPOTHESIS 95 



Avithin a country, when a species first arrives, is rapid, not slow. 

 But we have already seen that the evidence of introductions 

 (p. 24) forms a very broken reed upon which to lean. It only 

 shows that the spread may be rapid when the conditions have 

 been changed, and cannot be twisted into meaning that spread 

 is always rapid even in such circumstances. Even in Ceylon or 

 New Zealand, only a small proportion of the introductions have 

 spread rapidly, although the conditions have often been changed. 

 Nowhere is there any indication of a whole flora, or great part 

 of it, spreading in this rapid way, whereas in the case of an 

 island like Great Britain, near to a continent, the local flora is 

 simply a somewhat reduced edition of that of the continent, and 

 the flora of such an island as Ireland, a little farther out again, 

 is a reduced copy of that of Great Britain. One may even go 

 further, and find upon little islands off the coast of Ireland a 

 still further reduction of the Irish flora. 



A careful consideration of what has been said in Chapters ii 

 and V will lead to the conclusion that in general the dispersal of 

 plants into new areas must be exceedingly slow, so slow that 

 as a general rule one will notice little or no progress in a lifetime 

 of observation. One cannot regard this objection as sound. 



An objection often brought up is (28) that in many places 

 characterised by the presence of endemic forms there are many 

 genera composed of endemic sjjecies only. This very striking fact 

 has been termed "swamping" by Dr Sinnott, who proposes a 

 hypothesis to the effect that "the longer a successfully invading 

 species remains in an isolated area... the less common it tends to 

 become until it is actually 'swamped' out of existence — quite 

 the reverse of the ' age and area' idea." He suggests that " some 

 may simply be exterminated outright, and some by continual 

 crossing with new forms may ultimately lose their specific 

 identity." Cf. also Guppy (44, Chs. xxi-xxvii), who gives full 

 accounts of it. 



On the whole, the older and more isolated the region, the 

 greater is the proportion of such genera. Ceylon has 89 of 1027 

 (apart from actuafly endemic genera); New Zealand has 127 of 

 ♦329, the HaAvaiian Islands have 101 out of 256 genera. 



There is no doubt that the fact that genera are common in 

 these floras with endemics only, and no wides, is a feature which 

 requires explanation; but as the genera with endemics only 

 behave exactly hke those which also contain wides, or like the 

 endemic genera, the fact that it cannot at the moment be satis- 



